This invention relates to a vehicle for civil engineering work or some other work, equipped with a torque converter, with no steering wheel for turning the vehicle. As the technique for turning the vehicle of this type, it is generally known to engage and disengage the driving power to the running means on any side, by clutching, independently from the running means on the other side. However, such clutching operation is quite difficult and it is hard to properly turn the vehicle safely with a predetermined radius of turning curvature when the vehicle is running at high speed, thus causing turnover of the vehicle from time to time at such turning. At low speed running, on the other hand, it is often desired to turn the vehicle with as small radius of turning curvature as possible, but such turning operation is very difficult even for the operator of considerable skill. There have been no conventional means for automatically realizing safe mild turning of the vehicle at high speed running and desired sharp turning with small radius of turning curvature at low speed running.